Re: [PATCH for-5.0 3/8] acpi: cpuhp: spec: clarify 'CPU selector' register usage and endianness

[Laszlo Ersek <lersek@redhat.com>]

On 12/04/19 18:05, Igor Mammedov wrote:
> * Move reserved registers to the top of the section, so reader would be
>   aware of effects when reading registers description.
> * State registers endianness explicitly at the beginning of the section
> * Describe registers behavior in case of 'CPU selector' register contains
>   value that doesn't point to a possible CPU.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  docs/specs/acpi_cpu_hotplug.txt | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/docs/specs/acpi_cpu_hotplug.txt b/docs/specs/acpi_cpu_hotplug.txt
> index ee219c8..4e65286 100644
> --- a/docs/specs/acpi_cpu_hotplug.txt
> +++ b/docs/specs/acpi_cpu_hotplug.txt
> @@ -30,6 +30,18 @@ Register block base address:
>  Register block size:
>      ACPI_CPU_HOTPLUG_REG_LEN = 12
>  
> +All accesses to registers described below, imply little-endian byte order.
> +
> +Reserved resisters behavior:
> +   - write accesses are ignored
> +   - read accesses return all bits set to 0.
> +
> +The last stored value in 'CPU selector' must refer to a possible CPU, otherwise
> +  - reads from any register return 0
> +  - writes to any other register are ignored until valid value is stored into it
> +On QEMU start, 'CPU selector' is initialized to a valid value, on reset it
> +keeps the current value.
> +
>  read access:
>      offset:
>      [0x0-0x3] reserved
> @@ -86,9 +98,3 @@ write access:
>                   ACPI_DEVICE_OST QMP event from QEMU to external applications
>                   with current values of OST event and status registers.
>              other values: reserved
> -
> -Selecting CPU device beyond possible range has no effect on platform:
> -   - write accesses to CPU hot-plug registers not documented above are
> -     ignored
> -   - read accesses to CPU hot-plug registers not documented above return
> -     all bits set to 0.
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>